The present invention relates to a supporting mechanism for an optical disc driving device.
In an optical disc player, there is a limit to ability to accurately control the trucking servo and focusing servo against the external vibration applied from the outside and the internal vibration. In particular, in the case of the computer disc player, the vibration generated inside the player at high speed reading becomes problem.
FIG. 9 shows a device for damping the external vibration. As shown in the drawing, a main frame 4 is mounted on a box 1 by three elastic members 2 at corners. On the main frame 4, a turntable 6 and a spindle motor (not shown) for rotating the turntable are provided.
A pickup 5 for reading information recorded in a disc is slidably mounted on a pair of guide rails 11a and 11b. The pickup engages with a driving screw 8 so as to be moved in a radial direction of a disc loaded on the turntable 6. The driving screw 8 is connected to a rotating shaft of a stepping motor 9 so that the pickup 5 is moved along the guide rails 11a and 11b by the rotation of the driving screw 8.
In operation, the main frame 4 including various members mounted therein are vibrated by imbalance of the disc and others when the disc is rotated by the spindle motor. In particular, at high speed reading of information, the rotating speed of the disc is increased, and hence the vibration is accordingly increased.
Since the main frame 4 is mounted in the box 1 through the elastic members 2, the vibration transmitted from the main frame 4 to the box 1 is reduced. The external vibration transmitted to the box 1 is damped by the elastic members 2. Therefore, the quantity of vibration transmitted to the main frame 4 is reduced.
FIG. 10 shows a vibration model of the structure shown in FIG. 9, where the elastic member 2 has a stiffness of k and a coefficient of loss (viscosity) of xcexc, and a main frame device 20 has a mass of m.
There is a following relationship if external force is F and displacement of the main frame device is x,
md2x/dt2=Fxe2x88x92xcexcdx/dtxe2x88x92kx
If the equation of motion is solved under a condition, the relationship between the resonance frequency f0 and the mass m can be obtained. The resonance frequency can be expressed as follows.
f0=1/(2xcfx80)*(k/m)1/2
The ratio of the resonance frequency f1 for the box 1 of mass m1 to the resonance frequency f0 for the main frame device 20 of mass m0 is follows.
f0/f1=(m1/m1)1/2
If the mass m0 is multiplied by 2, the resonance frequency f1 becomes about 0.7f1.
Thus, the transmissibility can be expressed by the mass and the stiffness and the coefficient of loss of the elastic member. It is possible to obtain a desired transmissibility by selecting the mass, stiffness and coefficient of loss.
From the foregoing, it will be understood that in order to interrupt the transmittance of the external vibration to the main frame device 20, it is effective to reduce the stiffness of the elastic member 2 and to increase the mass of the main frame device supported by the elastic member 2.
However, it is desirable to reduce the size of the device. Since it is difficult to increase the mass of the main frame device 20, the stiffness of the elastic member 2 is reduced heretofore.
Thus, the external vibration can be damped.
However, the own vibration of the main frame 4 caused by the imbalance of the disc and others can not be damped since the stiffness of elastic member is reduced.
If the main frame vibrates, the pickup 5 mounted in the main frame 4 through guide rails 11a and 11b is vibrated. If the pickup vibrates, the servo operation for controlling the information reading operation may be disturbed. As a result, the information can not be accurately read out.
An object of the present invention is to provide a device which may damp an internal vibration caused by operation of driving mechanisms in the device.
According to the present invention, there is provided a supporting mechanism for an optical disc driving device, comprising, a box, a main frame provided in the box, first elastic members elastically connecting the main frame to the box, an optical disc driving device mounted on the main frame, the optical disc driving device including a spindle motor and a turntable securely mounted on a rotating shaft of the spindle motor, a sub-frame, and second elastic members elastically connecting the sub-frame to the main frame.